1. Technical Field
The invention relates to the field of keyless access control devices. In particular, the invention relates to a keyless device for controlling access to motor vehicles having a transceiver device, which is allocated to the motor vehicle, and a mobile transponder, which transceiver device comprises a plurality of transmitters (low-frequency transmitters), which operate in the inductive frequency range and are allocated to different sides of the motor vehicle, for the purpose of transmitting a low-frequency code signal (LF signal), and a receiver unit, which operates in the high-frequency range (HF-range), for the purpose of receiving HF-response signals from the transponder, and which transponder comprises a receiver for the purpose of receiving the LF-signal and comprises an HF-transmitter for the purpose of transmitting an HF-response signal upon receiving the LF-signal.
2. Background Art
Furthermore, the invention relates to a keyless method for checking access authorization in motor vehicles.
This type of device and method have been disclosed in the papers xe2x80x9cEin Fahrzeugsicherungssystem ohne mechanischen Schlxc3xcsselxe2x80x9d [a motor vehicle security system without a mechanical key] by Ch. Schneider and U. Schrey, published in: xe2x80x9cAutomobiltechnische Zeitschrift 96xe2x80x9d [automotive magazine 96] (1994) no. 5 and xe2x80x9cSmart-Cardxe2x80x94Abschied vom Autoschlxc3xcsselxe2x80x9d [The smart-cardxe2x80x94The end of the car key] by U. Schrey, Ch. Schneider and M. Siedentrop, published in: xe2x80x9cSiemens-Zeitschrift 1/96xe2x80x9d [Siemens-Magazine 1/96]. The access control device described in these documents consists substantially of a transceiver device, which is allocated to the motor vehicle, and of a mobile transponder. The transceiver device comprises three transmitters (LF-transmitters) which operate in the inductive frequency range and of which one transmitter is allocated to the vehicle door, another is allocated to the passenger door and the third transmitter is allocated to the rear of the vehicle respectively. The transmitting antennae of the LF-transmitters are integrated into the respective side doors or into the rear bumper. Each LF-transmitter is connected to the door handle, allocated to the respective door, or to the boot button in such a manner that upon actuation thereof, the LF-transmitter which is allocated to this region of the vehicle transmits a low-frequency code signal (LF-signal). In contrast, the remaining LF-transmitters remain inactive and do not transmit any LF-signals.
The transceiver device which is allocated to the motor vehicle is also equipped with an HF-receiver for the purpose of receiving an HF-signal from the transponder. The transponder response signal received in the HF-receiver influences a control device which is equipped with a processor and in which the received response signal, which has been received as a crypto-code, is decrypted and checked for validity. If a match is established, a corresponding control signal is transmitted to the respective door locking mechanism for the purpose of unlocking the particular door, of which the door handle has been actuated beforehand.
The transponder is provided in the form of a so-called access card having an LF-receiver and a low-power HF-transmitter. The inductive receiving antenna is designed as a frame antenna and the high-frequency transmitting antenna is designed as a printed circuit board antenna. The LF-signal received by the LF-receiver of the transponder is decoded in the transponder. A microprocessor which is allocated to the transponder then calculates the codeword, which is contained in the LF-signal, using a security algorithm and transmits the result by means of the HF-transmitting unit to the HF-receiver of the transceiver device allocated to the motor vehicle.
Transmitting LF-signals for the purpose of xe2x80x9cwaking-upxe2x80x9d the transponder serves to predetermine a functional radius limitation by virtue of the rapidly diminishing magnetic field. It is only possible to receive the transmitted LF-signal within one functional radius of 1.5 to 2 meters. This ensures that only those transponders which are actually located in this near-field region are woken up by the actuated LF-transmitter. The required actuation of a door handle or a boot button and the limitation of the functional radius serve to localize in a defined manner the transponder or the person carrying the transponder.
In order to render it possible to unlock the respective motor vehicle door as quickly as possible, modified door handle and lock mechanisms are used which render it possible for the door, on which the handle has been pulled, to open immediately. Even the provision of these type of mechanisms does not make it possible to shorten the period of time which the [sic] requires for the purpose of transmitting the data transmitted from the LF-transmitter to the transponder. This applies in particular if complicated crypto-codes are to be transmitted on this low-frequency path, since this type of approach requires a specific period of time owing to the low data transmission speed. However, the transmission of the decoded response signal of the transponder to the HF-receiver only slightly delays the beginning of the door release action.
A further keyless device for controlling access to vehicles is disclosed in DE 43 29 697 C2. This device utilizes a central LF-transmitter for the purpose of transmitting the low-frequency code signal. However, in the case of this device it is provided that the LF-transmitter transmits LF-signals cyclically in specific time intervals. Only when the transponder, which is allocated to the motor vehicle, is located in the functional radius of the LF-transmitter, is it woken up and transmits its response signal back. In order to trigger the release mechanism, it is not necessary in the case of this device to have to actuate a door handle or a boot button. Since it is not possible in the case of this device to localize the transponder for the purpose of unlocking merely specific doors, this access control device is only suitable for motor vehicles which have central locking. In the case of this previously known access control device the release action is occasionally subjected to a time delay as caused by virtue of the time required to transmit the possibly complicated LF-signal.
Furthermore, a keyless access control device is described in EP 0 767 286 A2. This system employs a mobile HF-transmitter which upon actuation of a transmission button transmits HF-signals to an HF-receiving unit, which is disposed in the motor vehicle, for the purpose of identifying an access authorization and for subsequently opening the vehicle doors. This mobile transmission part is also allocated an LF-transceiver unit which communicates with an LF-transceiver unit disposed in the motor vehicle, if the transmission part which is formed as a key is inserted into a corresponding lock in the motor vehicle, i.e. the ignition lock. The LF-communication serves to perform a predetermined dialogue; furthermore, energy is used over the LF-path for the purpose of charging up a battery which is allocated to the transmission part. Although this access control device is also a keyless access control device, it is still necessary, however, for an authorized user to actively operate the transmission button, in order to gain access to the motor vehicle. The only difference from a conventional way of locking the doors of a motor vehicle is that the transmission button is actuated instead of a lock.
On the basis of the prior art discussed in the introduction, it is, therefore, the object of the invention to propose a keyless device for controlling access to motor vehicles and to propose a keyless method of checking access authorization in motor vehicles, which device is not only suitable for unlocking individual doors or bonnets and boot lids but which also renders it possible to exchange complicated code and response signals without having to put up with any noticeable delay in the unlocking procedure.
On the one hand, this object is achieved by virtue of the fact that each LF-transmitter of the transceiver device, which is allocated to the motor vehicle, is allocated an LF-signal which can be differentiated from the remaining LF-transmitters and that both the transceiver device and the transponder are allocated an HF-transceiver unit for the purpose of performing on the HF-path a bi-directional question-response dialogue which checks the access authorization, wherein at least one HF-response signal of the transponder contains a response code, which identifies the respective LF-transmitter, upon reception of an LF-signal which is transmitted by an LF-transmitter.
Furthermore, this object is achieved in accordance with the invention by virtue of a keyless method of checking access authorization in motor vehicles comprising the steps of:
transmitting coded LF-signals within the inductive frequency range, by a plurality of LF-transmitters, of which one is allocated in each case to a side of the motor vehicle,
receiving and identifying the LF-signal by means of a transponder,
activating an HF-transceiver unit which is allocated to the motor vehicle,
activating an HF-transceiver unit which is allocated to the transponder,
performing a bi-directional question-response dialogue on the HF-path between the HF-transceiver unit of the motor vehicle and that of the transponder, which dialogue includes the transmission of a response code which identifies the respective LF-transmitter, from which the LF-signal has been received, and the transmission of a crypto-code from the transponder to the HF-transceiver unit which is disposed in the motor vehicle,
identifying the crypto-code by the transceiver device, and
opening one or several door locks corresponding to the particular door or doors, which is/are allocated the transmitted LF-signal and the LF-signal received by the transponder.
The transmission of different LF-signals which can be allocated to each LF-transmitter, which signal is received by the transponder and upon identifying the respective LF-transmitter is transmitted back in a response code to the transceiver device located in the motor vehicle, renders it possible to localize the transponder or the person who is carrying the transponder, without it being necessary to actuate a door handle or the like provided on the vehicle. The transponder is thus localized at the particular point in time, at which it is moved into the functional radius of an LF-transmitter. The LF-signal merely serves, so to speak, to xe2x80x9cwake upxe2x80x9d the transponder, wherein the wake-up signal is provided in the form of an LF-signal which is specific to each LF-transmitter. The signal or quantity of data which is/are to be transmitted can thus be reduced to a minimum.
The question-response dialogue between the transceiver device, which is allocated to the motor vehicle, and the transponder for the purpose of interrogating the access authorization is performed on an HF-path, wherein both the transceiver device, which is located in the motor vehicle, and the transponder comprise an HF-transceiver unit. By using an HF-path for the purpose of transmitting the actual signals which are provided for identification purposes, it is also possible to transmit complicated crypto-codes between the two units, without this causing the user to notice a delay in the unlocking mechanism. This feature significantly increases the system security which is also enhanced by virtue of the fact that the question-response dialogue only takes place on the HF-path if the transponder is located within the functional radius of an LF-transmitter and is thus coupled thereto in an inductive manner. It is provided that the question-response dialogue is interrupted if the said transponder goes beyond the functional radius, without an unlocking procedure having taken place.
Since the localization of the transponder and the question-response dialogue required for identifying the transponder are already in use when the transponder is moved within the functional radius of an LF-transmitter, for example by virtue of a user walking towards his/her motor vehicle, the remaining period of time it takes for the user to actually reach a vehicle door is used up for the purpose of carrying out the identification process. Taking as a prerequisite a functional radius of the LF-transmitter of 1.5 m and an approach movement of 1 m/s, in theory 1.5 seconds could be required for the identification process including the procedure of unlocking the respective door. This period of time is more than sufficient to be able to transmit even complicated crypto-codes via the HF-path in a question-response dialogue.
By the time the authorized user has arrived at the vehicle concerned, the door is always open.
The LF-signals of the individual LF-transmitters can be coded, for example, over different time slots. All of the LF-transmitters can transmit an identical LF-signal, wherein only one LF-transmitter transmits in each case its signal in a predetermined time interval, which is followed by a defined pause before a second LF-transmitter transmits its signal. This sequence is repeated in a cyclical manner over the number of LF-transmitters which are used. If a response signal from the transponder is received at a time close to the LF-signal of an LF-transmitter, it is possible to allocate the received response signal to the particular LF-transmitter which was the last one to transmit an LF-transmitter [sic]. It can be provided that upon reception of a response signal from the remaining LF-transmitters it is initially not possible to transmit any further LF-signals. In contrast, for the purposes of localization control, the particular LF-transmitter, which has been allocated the response signal, will transmit LF-signals once again.
In a further embodiment it is provided that the LF-signals of the individual LF-transmitters comprise a different code, so that code-dependent localization takes place.
In the case of cyclically transmitted LF-signals, it can be provided that the HF-transceiver unit is activated during transmission of the LF-code signal and is then powered down after a predetermined delay-time, if in the meantime no response signal has been received.
The LF-range is expediently located between 1 and 135 KHZ and lies, in particular, between 1 and 25 KHZ. It has been demonstrated that the low-frequency transmission frequencies are more insensitive in particular with regard to disruptive influences of the motor vehicle bodywork. If the transmission frequencies are above 135 KHZ, the vehicle bodywork can have an extremely unfavourable effect upon the functional radius of the LF-transmitters. The HF-frequency range is expediently between 100 MHZ and 10 GHZ.
In a further embodiment it is provided that the transceiver device which is allocated to the motor vehicle has a number of directional antennae corresponding to the number of LF-signals for the directional reception of the HF-response signals of a transponder, wherein the directional antennae are directed in the particular direction, in which the LF-transmitters transmit away from the motor vehicle. This type of feature renders it possible to achieve double localization of the transponder, wherein the first localization is achieved by way of the LF-transmitters and a further localization is achieved by way of the reception direction of the HF-response signal.